The following relates to the lighting arts. It especially relates to flip-chip bonded group III-nitride light emitting diodes for lighting applications, and will be described with particular reference thereto. However, the following also finds application in conjunction with other types of group III-nitride light emitting diodes, and in other group III-nitride optoelectronic devices such as vertical cavity surface emitting lasers (VCSELs).
In the flip-chip mounting configuration, a light emitting diode with a light-transmissive substrate is bonded “face down” to bonding bumps of a mount, that is, with the epitaxial layers proximate to the mount and the light-transmissive substrate distal from the mount, to make electrical and mechanical connection to the mount. The flip-chip arrangement has a number of advantages, including improved thermal heat sinking due to the proximity of the front-side active layers to the heat sinking mount, and elimination of electrode shadowing losses.
In the case of group III-nitride light emitting devices, formation of an economical and robust p-type electrode that has good electrical and reflection properties is difficult. Aluminum has the advantage of being highly reflective; however, aluminum has a low work function and a large contact resistance with respect to p-type gallium nitride.
A nickel layer is sometimes inserted between the p-type gallium nitride and the aluminum to improve electrical characteristics. While having good electrical characteristics, such nickel/aluminum contacts still exhibit less than ideal reflectance characteristics due to light absorption in the nickel.
It is also known to employ silver in contacting p-type gallium nitride. However, silver is more expensive, and exhibits poor adhesion to p-type gallium nitride. Moreover, silver migration can occur under certain operating conditions. The migrating silver can short the p/n junction, causing catastrophic failure of the device.
The present invention provides a new p-contact and method for making a p-contact that overcomes the above-referenced problems and others.